1. Field of the Invention
The present invention relates to a method of blasting wherein one or more explosive thrusts are generated in rock in directions in which the rock has been found to be particularly vulnerable to failure.
2. Description of the Prior Art
Blasting processes have long provided man with a powerful tool for performing useful work, affording the energy required, for example, for excavation operations of various kinds, i.e., operations in which material is dug out and removed at or below the earth's surface either to form a useful cavity or to derive profit from the removed material, e.g., in mining. More recently, blasting processes for fracturing deep rock have become increasingly important as it has become necessary to tap deep mineralized rock masses, e.g., ore bodies or oil or gas reservoirs located from about 100 feet to about a few thousand feet beneath the earth's surface, in order to supplement or replace dwindling energy sources and minerals supplies. The fracturing procedure is required to prepare the masses for such in situ recovery operations as leaching of ore or retorting of oil shale in place.
The preparation of large volumes of deep rock for in situ operations by blasting requires the emplacement of enormous amounts of explosives in the regions to be fractured, which in turn entails the drilling of vast numbers of shot holes therein. To some extent, drilling costs can be reduced by drilling holes of smaller diameter than is required to accommodate the size of the explosive charges to be employed, and enlarging or "springing" the lower parts of the shot holes, located in the segment of rock to be fractured, to produce chambers having the volumes required to hold the explosive charges. Nevertheless, the costs of such large blasts will be substantial. Therefore, any procedure which can increase the effectiveness of the blasting process, i.e., produce more useful work (e.g., fracturing) in a given volume of rock per weight of explosive used, and thereby allow larger separations between shot holes or a smaller explosive charge per shot hole would add considerably to the value of the blasting process.